1. Field of the Invention
This invention relates to improvements in laser gyroscopes, and more particularly to circuits for increasing the resolution of a laser gyroscope.
2. Description of the Prior Art
Laser gyroscopes are known in the art to produce outputs comprised of optical pulses occurring at a rate dependent upon the rate of rotation of the laser gyroscope. Typically, two outputs are developed from a photodiode array which detects the optical frequency difference of clockwise and counterclockwise laser beams within the gyroscope. A laser gyro it typically equipped with a readout assembly having combining optics for extracting and combining a small percentage of light from each of the counter rotating beams and for focusing the combined light onto a photodiode array. A low noise amplifier amplifies the signals. The amplified signals are shaped to provide a two phase revolver type signal wherein one signal leads the other or lags the other by 90 degrees, depending upon the input axis rotation of the gyroscope. One circuit which has been advanced includes a pulse modification circuit for each output line including a preamplifier and squaring trigger together with logic circuitry to produce a first output representing clockwise pulses and a second output representing counterclockwise pulses. In the past, the output pulses produced tracked, one for one, the output pulses of the gyroscope; consequently, the resolution of the entire circuit has been limited by the pulse output frequency developed by the gyroscope.
A prior art circuit titled: "APPARATUS FOR INCREASING THE RESOLUTION OF A LASER GYROSCOPE", Ser. No. 457,845, filed Jan. 14, 1983 having a common inventor and assignee performs the required decoding and frequency multiplying of A quad B type signals as are typically output by a laser gyro. The circuit of this prior reference is self clocked by the input A quad B signals and provides clock and counter mode control signals to an up-down counter at purely random times with respect to the navigational system's system clock. Unsynchronized operation of this character may result in a readout from the counter that occurs at the same time that a clock pulse is being counted. Indeterminate states may result. In addition, the one-shots integrated circuits used in the prior art circuit are subject to noise pulses accompanying the input signal.
This invention circuit provides a synchronous A quad B decoding and enhancement circuit that does not require one-shots in its mechanization.